Climate change is expected to devastate coral reefs, as warmer oceans are believed to be inhospitable to corals. But corals may be more robust than commonly thought. A number of studies have found coral colonies that endure high water temperatures. Now, a team of scientists has taken a step toward identifying the genetic mechanisms that might be giving some corals a natural resilience to thermal stress.

Coral reef ecologist Daniel Barshis and colleagues at Stanford University took advantage of markedly different environmental conditions in two nearby but separate pools on a reef at Ofu Island, American Samoa. Because of local factors that isolate some areas of the reef from winds and waves that might mitigate temperature extremes, some pools in the reef are highly variable in temperature, with summertime water temperatures topping 93 degrees Fahrenheit, which – depending on other factors – can trigger bleaching, or a damaging loss of the symbiotic algae that corals depend on.

Yet Acropora hyacinthus, a common reef-building coral found in these pools, grows faster and is more thermally tolerant than corals of the same species in nearby pools that do not get as hot. The team took samples of corals from both the highly variable and the moderately variable pools and subjected them to thermal stress experiments under laboratory conditions while monitoring the levels of expression, or activity, of a wide range of genes.

The researchers identified 60 genes with an unusual expression pattern. Under normal temperatures, these genes were more active in the corals from the highly variable pool. But when water temperatures rose, they were more active in the corals from the moderately variable pool. “We’re not really sure if the tolerance is a direct result of the activity of these genes or an associated factor,” Barshis says. But perhaps the higher gene expression under normal conditions – which the team calls “frontloading” – prepares these resilient corals for periodic hot water, the team reports in the Proceedings of the National Academy of Sciences.

Barshis calls the findings preliminary because of the complexity of coral biology.

Still, Barshis says, the study “somewhat paints a hopeful picture” for coral reefs. He suspects that, like the Ofu reef, most major reefs harbor high-temperature habitats that may be fostering the diversity needed for corals to survive extreme temperatures.